The invention relates generally to dynamically-varied beam energy using a tunable monochromatic x-ray beam. For example, in radiation therapy the energy of such an x-ray beam can be varied during treatment to compensate for changes in the position of a tumor relative to a beam source and the body of a patient such that an optimally minimal effective dose of radiation is administered.
Various radiation therapies, or radiotherapies, including, for example, intensity modulated radiotherapy (IMRT), image guided radiotherapy (IGRT), proton therapy, electron beam therapy, and gamma knife treatments are known. Such radiotherapies typically require that lethal doses of radiation be applied to a tumor for the treatment to be effective, and such radiotherapies typically are planned and delivered in a fashion using one specific beam energy for any given therapy session. These doses of radiation are problematic, however, because they are as lethal to normal tissues as they are to tumors. The doses of radiation administered in such radiotherapies are predominantly distributed throughout a tumor's tissues in a pattern that is somewhat random on a microscopic or intracellular level. This results in singlet oxygen and other ionized compounds that are damaging to intracellular organelles of both the tumor tissues and surrounding healthy tissues.
Furthermore, because these radiolytic events are random, they may or may not lead to severe damage to the DNA that resides in the nucleus of a tumor's cells. Additionally, much of the damage induced by known radiotherapies can be repaired by the cell or, alternatively, the cell itself may not be sensitive to the radiation in certain phases of its reproductive life. These characteristics of radiolytic events and cell development typically require that large doses of radiation are given repeatedly in multiple sessions over several days or weeks to effectively destroy the tumor cells.
Auger Cascade Radiotherapy (ACR) is an alternative radiotherapy that uses non-lethal doses of radiation and is less random than other current radiotherapies. ACR entails incorporation of target atoms having high atomic number onto or into the double helical structure of the DNA of tumor cells. A monochromatic photon beam, for example an x-ray beam, with an energy at or slightly above the binding energy of the inner electron shells of the target atoms and directed at the tumor can displace or eject electrons from the inner suborbital shells of the target atoms. The displaced electrons become photoelectrons that distribute their energy within nanometers of the DNA onto which the target atoms are incorporated, resulting in damage to organelles and breaks in the double helix structure of DNA in surrounding cells. The displaced electrons leave voids in the orbits from which they are ejected. These voids are filled by electrons that tend to cascade from higher energy orbits into the voids. As electrons from higher energy orbits cascade into the voids left by the displaced electrons, energy corresponding to the difference in the energy level of the higher level orbit and the energy level of the orbit from which the electron was displaced is emitted in the form of photons. These photons also distribute their energy within nanometers of the DNA onto which the target atoms are incorporated. The cascading electrons also leave voids in their original orbits, which are similarly filled by cascading electrons from even higher energy orbits. This cascading process is known as Auger cascade.
The repeated emission of photons from the target atoms during Auger cascade results in very intense localized radiation within a few nanometers of the target atoms. Because ACR is less random and more localized that other radiotherapies, and because it uses energy emitted from stimulated target atoms, far less external radiation is necessary for effective treatment. Typically, the dose of external radiation required is three to five time less than a dose lethal to surrounding tissues.